Project Summary: Despite advances in the development of HIV drugs there remains a need for new therapies. Toxicities associated with long term use of many of the approved HIV drugs coupled with the development of resistance drives the need for new and novel antivirals. Maturation inhibitors (MIs) represent one such class of HIV therapies. HIV maturation inhibitors block virus replication by disrupting the conversion of the capsid precursor protein, CA-SP1 (p25), to the mature form of capsid, CA (p24) resulting in the formation and release of non- infectious viral particles. Unlike protease inhibitors that bind to and inhibit the action of the viral protease, MIs directly target the HIV-1 Gag protein. This novel mechanism of action allows MIs to retain full activity against viruses that have developed resistance to approved classes of HIV drugs. Clinical proof-of-concept for maturation inhibitors was established with the first-in-class MI, bevirimat (BVM). In a series of trials, BVM was shown to be safe and effective in reducing HIV viral load in infected individuals, however, a lack of uniform patient response was also observed. Analysis of patient virus revealed that a single amino acid polymorphism in the SP1 region of the viral Gag protein was a primary determinant of patient response. This polymorphism involves a Val to Ala change at SP1 amino acid 7: V7A. Approximately 50% of HIV-1 isolates contain V7 and are highly sensitive to BVM while the remaining 50% contain A7 and lack sensitivity. As a result of this observation, clinical development of BVM was terminated. DFH Pharma's current efforts focus on the identification of next generation MIs with broad anti- HIV activity. Specifically, we have identified 2nd generation MIs that exhibit potent activity against a range of HIV isolates. Unlike the restricted activity observed with BVM, these 2nd generation analogs inhibit a broad variety of group M subtypes, group N and O viruses and isolates resistant to currently approved HIV drugs. Recent testing has determined that the most potent of these broadly active compounds exhibit IC50 values in the single digit to low double digit nM range. This activity level is within the accepted range for HIV drug development candidates and compares favorably with the Bristol-Myers-Squibb (BMS) MI clinical candidate. The focus of the current application is to build on this success and continue the effort to identify 2nd generation MIs suitable for development as HIV drugs. Having identified compounds that are both highly potent and broadly active the objective of the proposed work involves further characterization of the drug development potential of the most promising compounds to select 2nd generation MIs to advance into IND-enabling pre-clinical studies.